for x in `seq 0 255`; do
  for y in `seq 0 255`; do
    ssh root@192.168.$x.$y 'yum install program'
  done
done

#!/bin/bash

# File containing hostnames for all the servers; one per line.
serverlist=~/.server-list
[ -r "$serverlist" ] || exit 1

# Create a safe, autodeleted temporary directory
work=$(mktemp -d) || exit $?
trap "rm -rf '$work'" EXIT

# List of hosts to connect to
hosts=()
while read host dummy ; do

    # Ignore comments
    host="${host%%;*}"
    host="${host%%#*}"
    host="${host%%/*}"
    [ -n "$host" ] || continue

    # Add host to hosts used
    hosts=("${hosts[@]}" "$host")
done < "$serverlist" || exit $?

# None?
[ ${#hosts[@]} -gt 0 ] || exit 0

# Run remote commands in parallel on each host.
for host in "${hosts[@]}" ; do
    ( exec </dev/null >"$work/$host.out" 2>"$work/$host.err"
      echo -n "Started "
      date
      ssh "$host" "$@" && echo "[OK]" || echo "[Error $?]"
      echo -n "Finished "
      date
    ) &
done

# Wait for all to complete
wait

# Output the summary of all commands
for host in "${hosts[@]}" ; do
    echo "Output from $host:"
    sed -e 's|^|\t|' "$work/$host.out"
    echo ""
    if [ -s "$work/$host.err" ]; then
        echo "Errors from $host:"
        sed -e 's|^|\t|' "$work/$host.err"
    else
        echo "No error messages."
    fi
    echo ""
    echo "========================================"
fi